title: Vibrational energy flow between modes by dynamic mode coupling in THIATS J-aggregates.
abstract: We performed ultrafast pump-probe spectroscopy of J-aggregates of 3,3'-disulfopropyl-5,5'-dichloro-9-ethyl thiacarbocyanine triethylammonium (THIATS), one of the most typical cyanine dyes, and detected excited molecular vibrations, using a sub-10 fs pulse laser. The time-resolved two-dimensional difference absorption (ΔA) spectra are observed between -314 and 1267 fs. By performing the Fourier transform and spectrogram analysis, vibrational modes in THIATS are observed at 285, 485, 555, 824, and 1633 cm(-1) and there was a modulation of the vibrational frequencies around 1633 cm(-1) which depend on the delay time, respectively. By the analysis of the modulation, energy flow is found to take place from other modes to the 1633 cm(-1) mode through the low frequency mode with ∼50 cm(-1). Also, by fitting the real-time traces of ΔA with the sum of two exponential functions and a constant term, the average lifetimes of three electronically excited states were found to be τ1 = 52 ± 5 fs and τ2 = 540 ± 78 fs. By performing single-exponential fitting around the stationary absorption peak at 1.990 eV, in the negative time range, the electronic dephasing time, T2(ele), is determined to be 18.30 fs.
authors.affiliation: Department of Physics, Faculty of Science, Tokyo University of Science , 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Hasegawa
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Nakata
authors.forename: Eiji
authors.initials: E
authors.lastname: Tokunaga
authors.forename: Kotaro
authors.initials: K
authors.lastname: Okamura
authors.forename: Juan
authors.initials: J
authors.lastname: Du
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Kobayashi